This application relates to a method and apparatus which, according to the preferred embodiment disclosed herein, permits the spinning of yarn at a constant tension. Also according to the particular embodiment disclosed in this application, the method and apparatus relate to a cotton-system ring spinning frame of conventional design which is modified to operate according to the method and apparatus described. The application has use in many other fields, however, and may also be used, generally, to vary the speed rate change of a driven member having a high inertia load to accomodate finite power availability from a prime mover, such as a motor.
Conventional spinning frames operate at a constant spindle speed. Power is typically provided from a constant speed electric motor through a fixed gear train to the spinning frame cylinder, which typically runs the entire length of the spinning frame between the two opposing banks of spindles. Individual tapes or belts transfer power from the cylinder to spindles along the length of the spinning frame. As the spinning operation takes place, yarn roving is delivered from a supply package to the drafting zone of the spinning frame which generally comprises two or more sets of rollers which rotate at different speeds to elongate the roving as it passes from between one set of rollers to another. Twist is inserted into the yarn by passing the yarn under a traveler which rotates at high speed around a ring which surrounds the spindle on which the receiving bobbin is placed. In order to evenly distribute the newly twisted yarn along the length of the bobbin, the spinning frame ring rail reciprocates upwardly and downwardly according to a pre-determined pattern so that the yarn is placed on the bobbin in a desired manner. During the reciprocating motion of the ring, the tension on the yarn varies considerably. A relatively rapid variation in tension occurs as the ring rail reciprocates due to the constantly changing height of of the balloon created by the yarn being spun rapidly around the spindle by the traveler. Variation in the yarn package diameter caused by the winding pattern, i.e., filling wind, combination wind, etc., also causes a corresponding variation in yarn tension. Tension also varies considerably depending on a number of other well known variables.
Care must be taken to ensure that tension on the yarn during the entire spinning operation never exceeds the maximum tension which the yarn will withstand without breaking. This maximum tension must be pre-determined and the spindle speed of the spinning frame must be adjusted so that the maximum tension which the yarn will tolerate is never exceeded. In practice, the yarn is spun at a tension well below the maximum which can be applied to the yarn in order to provide a margin of error.
Care must also be taken on a conventional spinning frame to ensure that the yarn is spun above a minimum tension below which the yarn is weakened and not suitable for further processing. Since on conventional spinning frames the spindle is rotated at a constant speed, the tension constantly vaies between the upper and lower limits which have been previously established. This constant tension variation during the yarn spinning process is very unproductive. Tension variation on the yarn reveals itself in later processing, expecially in dyeing where variations in yarn tension can create variations in dye absorbability. As is well known, a variety of other defects can arise as a result of extreme variations in tension.
Aside from the decrease in yarn quality, overall productivity of yarn production is adversely affected, since under lower tension the yarn is not wound tightly on the bobbin. A looser wind on the bobbin also results in more frequent doffing. Of course, the machine is not running as long between doffs and more labor is required to doff the spinning frame more frequently. Loosely wound yarn is also subject to "sluffing off" during later processes.
In general, spinning yarn in the conventional manner with constantly increasing and decreasing tension results in a yarn having uneven cross-section--thus a lack of tensile strength uniformity. It has been determined that spinning yarn at a constant tension throughout the entire process results in a yarn having a more uniform cross-section and a tensile strength approximately 10% higher than equivalent yarn spun at a constant speed.